What I find really goofy is that it's doubly disabled. First, you have to drag it over into the modpack yourself. Then, once it's in, you have to generate a world of BoP by selecting it (e.g. Normal, Large Biomes, Flat, BoP). Maybe that's because BoP is a multi-faceted mod in that it adds stuff *and* biomes, so if you don't generate a BoP world, you still have some BoP stuff (like bushes), but it still seems weird to me.